As an example of the basic structure of an information recording medium with respect to which information is optically recorded, erased, rewritten, and/or reproduced, there is an embodiment in which a second dielectric layer, a recording layer, a first dielectric layer, and a reflective layer are disposed in this order from the optical beam incident side, for example. Conventionally, (ZnS)80 (SiO2)20 (mol %) has been used as a material for the first and second dielectric layers, for example. This material is an amorphous material, and has low thermal conductivity, high transparency and high refractive index. Further, it has high deposition rate in film formation, and has excellent mechanical properties and moisture resistance as well. Thus, this material has been put to practical use as a material suitable for forming dielectric layers.
However, in the case where this material is used for dielectric layers in a rewritable information recording medium, when repeated rewriting is performed by irradiating the recording layer with a laser beam, S in the (ZnS)80 (SiO2)20 (mol %) is diffused in the recording layer, thereby causing a significant decrease in the repeated rewriting performance, which is a problem. In order to solve this problem, there has been adopted a structure in which another dielectric layer (interface layer) with a thickness of about 5 nm is additionally provided each between the first dielectric layer and the recording layer, and between the recording layer and the second dielectric layer (see, for example, Patent Literature 1).
For example, Blu-ray disc (hereinafter, abbreviated to BD) media that have been put to practical use as a recording medium for high definition images use a material containing ZrO2—Cr2O3 (hereinafter, referred to as Zr—Cr—O) for interface layers, and achieve excellent, 10,000 or more times repeated rewriting (see, for example, Patent Literature 2). This material is free from S. It has high melting point and excellent heat resistance, and further has good adhesion to the recording layer. Therefore, it is a material suitable for interface layers. When a BD medium is provided with a plurality of information layers that are referred to as L0, L1, . . . , sequentially from the opposite side of the optical beam incident side, the translucent information layer (L1) located on the optical beam incident side, particularly in a two-layer BD medium with a capacity of 50 gigabytes (GB), has a structure in which very thin layers such as a recording layer with a thickness of about 6 nm and a reflective layer with a thickness of about 10 nm are stacked. In such a structure, the use of interface layers made of Zr—Cr—O has enabled such 10,000 times repeated rewriting performance to be achieved.